Well when you load up SC, you see the campaign editor. Open that and u get a new window loaded up. That is where all the map making work will be placed. On your left side you have at the top, a Mini map to show you map so far. Along the left side, Your Terrain,players 1-8 (Buildings, Units, Starting Location, and much more), Resources (Minerals, Gas, Other extras), and if you progress to a more advanced Editor, Extras. For yor first map, I suggest just making a melee map. MAke some obstacles (Hills, holes, ect.), then make minerals, and gas for each player u will have. After you finish that, you will making starting location (Which can be found in the left side throughout the 1-8 players.) for each player at their particualr starting spot. Start with tha, and work off it. Check some actual map making sites, and the people at BF's about trigger (used for use map settings maps) !!!! HOPE THIS HELPS!!!
-Desroches